This invention relates to an improved foundry core mix. In a more particular aspect, this invention relates to components of an improved core binder system.
Cores useful in making metal castings are customarily made by placing a foundry aggregate, usually silica sand which has been admixed with a suitable binder, against a shape or pattern and then hardening the binder, as by polymerization. The resulting core is a self-supporting structure which forms a part of a mold assembly.
Various sands are used for making cores. The cores themselves are made by a variety of processes employing a wide variety of binders. Three of the many processes in commercial use today are the so-called cold box process, no-bake process and the rapid no-bake process. The cold box process is one in which sand is admixed with a suitable resinous binder composition, blown into a core box, and then gassed with a suitable vapor phase catalyst to cure the binder. By such process, which is described for example in U.S. Pat. No. 3,409,579, a core of sufficient hardness to be stripped from the core box is produced in a matter of seconds. The no-bake process is one in which a resinous core binder is admixed with a catalyst and sand and placed in a core box. The core cures at ambient temperatures but much more slowly than in the cold box process, over a period of hours or even days. After a suitable period of time, such as two hours, the core can generally be stripped from the core box, but requires further cure time. The rapid no-bake process is similar to the no-bake process, but the character of the resin and the amount and type of catalyst employed are such that a core is formed and may be stripped from the core box in a matter of a few minutes. The bench life, or time period during which a sand-resin mixture may be kept before the reaction proceeds to a detrimental extent prior to placing the mixture into the core box, generally decreases rapidly when the catalyst and resin are adjusted to provide very rapid set times. Therefore, the development of the rapid no-bake process was dependent upon the availability of foundry machines which were capable of mixing small but accurately controlled amounts of resin, catalyst and sand and transferring the admixture substantially immediately into a core box. Processes of this type are described, for example, in U.S. Pat. No. 3,702,316.
The subject invention provides a binder system which is suitable for use in all three of these processes by adding a suitable catalyst immediately before use. It will be understood that the kind and amount of catalyst employed will be such as to adapt the final binder-sand admixture to the intended purpose. That is, in the cold box process, the catalyst will typically be a gaseous amine, such as triethylamine, dispersed in a suitable carrier such as carbon dioxide. In the no-bake and rapid no-bake process, amine catalysts and conventional metal catalysts such as lead naphthenate or dibutyl tin dilaurate are employed in amounts adjusted to provide the desired set time.